A time study was undertaken combining morphological methods with tracer studies on the entry of herpes type viruses into cells and subsequent early intracellular events have been followed by electron microscopy. Tracer studies were utilized to follow the incorporation of viral DNA into preformed empty nucleo capsids upon removal of an inhibitor of DNA synthesis. Structural differences of the viral core of various herpesviruses could be visualized by using different stains and fixatives on virus infected and transformed cells. Mice with subcutaneous transplanted tumors were treated 7 days later with a synthetic agent (pyran copolymer). Controls received 0.9% NaC1. In vitro and histopathologic studies on activated macrophages of the host and tumor biopsies revealed the important role of these cells against tumor tissue. The drug therapy resulted in (a) enhanced macrophage inhibition of tumor cell DNA synthesis, (b) heavy accumulation of macrophages and histiocytes at the site and (c) association of histiocytes with tumor cells. BIBLIOGRAPHIC REFERENCES: Schultz, R. M., Papamatheakis, J. D., Luetzeler, J., Ruiz, P. and Chirigos, M.: Macrophage involvement in the protective effect of pyran copolymer against the Madison lung carcinoma (M109). Cancer Res. 37, 358-364, 1977.